Wohooo! managed to install new (used) rear caliper, and change both rear discs and pads. And the brakes still work

All I can say is rewinding 10 year old rear calipers is a pig of a job. That first turn until they get going is almost impossible unless you are a body builder.
I think it helped to open up the bleed valve to let the fluid out locally, it just wouldnt budge with the bleed valve closed. It doesnt help that you cant hold the caliper properly whilst its still attached to the cables/hoses.
When I add up all the tools I had to buy (new torque wrench thats more accurate,etc), plus the discs and pads, the whole job comes to around £250.
(Febi discs were only £40 from incarmotorfactors, Bosch pads were only £12 from ebay)
Still its very satisfying to do a job yourself.